ACTUALITÉS ET ÉVÈNEMENTS

Avoiding Collisions on the Track

In Roswell, Georgia, residents make their way down tree-lined brick walkways of the city’s Historical District, sipping their morning coffee from recycled paper cups, gazing at furniture through shop windows. Just outside of this city founded on manufacturing mills is Andritz Inc., an international provider of services and equipment for the world’s creators of pulp, paper, tissue, and Oriented Strand Board (OSB) products including furniture and homes.

With more than 150 years of experience, Andritz is able to support pulp and paper companies with a complete top-to-bottom custom integration process. Andritz provides equipment for the processing of short wood, bunk wood, and tree-length logs using debarking drums, chippers, conveying and storage systems, refiners, pulp drying lines, and tissue paper machines that form, press, dry, and reel the finished product. From start to finish these applications are designed, set up, programmed, delivered, and installed by Andritz for the customer.

Project Details

In 2006 Andritz was commissioned for two different OSB Mill projects: one requiring the installation of four portal cranes at Grant Forest Products in South Carolina, and another requiring two portal cranes at Martco Industries in Oakdale, Louisiana.

The portal cranes in both projects were to be used for unloading logs from logging trucks and transporting the materials to an onsite woodyard. The cranes would need the ability to operate independently and simultaneously while sharing a common set of two perpendicular rail tracks. This system would enable the two cranes to travel from the log truck unloading area to the woodyard infeed equipment or to the log storage area located between the two rails.

“Andritz has portal cranes capable of lifting an entire load of tree-length logs from a logging truck with a single bite of the grapple,” notes Robert Dunlop, Sr. Electrical and Automation Project Engineer for Andritz, who is responsible for the electrical and control systems of these cranes.

Many of these portal crane grapples can lift up to 44 tons of logs in a single bite and transport them along rail runways sometimes up to a mile in length. Cranes traveling high speeds can safely operate up to 750 feet per minute (12.5 feet per second).

“A typical portal crane unloading and delivery cycle is about 2.5 minutes per crane, translating into hundreds of tons of wood per hour being processed,” Dunlop said.

The Challenge

Given the high performance demands of modern crane applications, the old practice of using 300- to 400-foot bus bars or festooning cables to communicate between the gantry and trolley was not an option.

“Festooning cables and bus bars are costly and are a frequent source of operational problems. It can cost around $10,000 for materials alone, plus installation and maintenance costs. Then when the equipment fails, downtime is a serious problem to a customer and can sometimes take a day to repair,” Dunlop explained.

The bus bar systems operate on a serial communication network so data rates are slow, and during poor weather, particularly precipitation, the signal is often degraded. Even if the serial communication system was faster, bus bars can only communicate from gantry-to-trolley and not from crane-to-crane, which is needed for anti-collision systems.

Each crane costs millions of dollars and for the safety of the crane operators it is imperative to have a reliable anti-collision system in place. Andritz needed the ability to monitor the real-time location of each crane on the rails and to automatically slow down and stop each crane should it enter a potential collision situation. Until the advent of wireless devices, safe and reliable anti-collision systems were just wishful thinking.

The Solution

Andritz placed a satellite GPS system on each crane to accurately determine their respective locations on the rail. For this to be an effective solution, each crane would need to know the position of the other crane. Andritz selected ProSoft Technology’s Industrial Hotspot radios as their wireless solution.

ProSoft Technology’s radios provide the speed needed to transfer data between the cranes and the operators in real time. They are certified for harsh environments, making them a dependable solution despite poor weather conditions.

“I use ProSoft’s radios all the time for this type of application,” Dunlop said. “The main advantage of using high-speed Ethernet radio systems is that they help the cranes avoid collisions on both the network and on the track. Plus, operating wirelessly creates a significant cost savings by eliminating additional communication bus bars and festooning cables.”

Altogether, the two projects utilized twenty radios: thirteen radios for the Grant Forest Products project and nine for Martco Industries.

One radio is attached to each crane and is dedicated to communicating its GPS position to the other crane on the tracks. A set of radios then connects each crane’s gantry control system to its trolley control system.

“The high-speed Ethernet communications are very effective, so that when the crane operator moves the joysticks inside the operator cab, the gantry and trolley controls respond seamlessly, without any noticeable delays,” Dunlop explained.

Finally, a radio was implemented to connect the control systems for each application to a woodyard ground station on site, where a Rockwell Automation® ControlLogix® platform manages the data. The ground station radio allows for remote troubleshooting, programming, and operational data acquisition of the cranes. It also allows Andritz to provide remote crane diagnostics and programming support through internet connections.

Results

The Grant Forest Products and Martco Industries projects were live as of October 2006 and January 2007, respectively. In application, the two wireless systems not only created a more efficient, cost-effective network than bus bars and festooning cables, but are far more reliable in diverse weather conditions. The wireless networks are self-healing, with significantly less risk of signal degradation than the alternative, and they operate in real time, which is key to a successful anti-collision system.

With sophisticated processes involving multimillion-dollar portal cranes operating at rapid speeds while carrying several tons of materials, crane collision is a clear concern. It is not only the cost of downtime and repair to be considered, it is the safety of the crane operators and workers on the ground level that is also of importance. In these cases, a real-time wireless Ethernet network was the only way to facilitate the conditions needed for a high-performance anti-collision system. The networks created by Andritz will protect the portal cranes, thus creating a safer environment for crane operators and workers on the ground level.